Heretofore picture frames, signboards, building plaques and the like have been made using plaster, mortar, portland cement concrete, and sheets of synthetic resin. Some have hollow, honeycomb-type or foamed polymer core structures. U.S. Pat. Nos. illustrating such articles include: 306,462; 1,204,613; 1,675,580; 3,186,118; 3,373,517; and 3,704,535. In general they lack some desirable feature such as longevity, freedom from maintenance, durability especially against stress cracking, low unit weight, and a wide variety of design options as to structure, shape, color, size, indicia, or expression of artistry. The present invention brings to the sign market a capability to have all of these desirable features at a reasonable cost.
Polymer-fortified concretes containing portland cement, compounded aqueous synthetic resin latex emulsion, aggregate, and water have been proposed as a dry set hydraulic cement for tiles, for improving the flow of cement and mortar pastes, particularly those containing lime, for water control, bonding and repairing to other materials such as concrete substrates, for blister-resistance, and for shrinkage compensation and resulting freeze thaw durability in expansive aluminate-type cement compositions. By a polymer-fortified concrete here is meant one compounded with such aqueous latex, portland cement, comparatively fine aggregate such as sand, and usually some water to supplement the aqueous latex.
However, the special advantages of using polymer-fortified portland cement concretes for making signboards (particularly concretes containing type 1 non-air entraining cement and no added lime) has not heretofore been recognized, and neither has incising the sign indicia into the set up, but not yet practically cured or hardened concrete sign surface. The polymer fortification of the concrete sign gives it good strength, dimensional stability, and weather tightness in comparatively thin sections, even one having substantial surface area (e.g. 6-10.sup.+ feet across).